1. Field of the Invention
The present invention relates generally to semiconductor switches, and relates more particularly to bidirectional semiconductor switches produced in a III-Nitride material system.
2. Description of Related Art
Development of devices based on III-nitride materials has generally been aimed at high power-high frequency applications such as emitters for cell phone base stations. The devices fabricated for these types of applications are based on general device structures that exhibit high electron mobility and are referred to variously as heterojunction field effect transistors (HFETs), high electron mobility transistors (HEMTs) or modulation doped field effect transistors (MODFETs). These types of devices are typically able to withstand high voltages in the range of 100 Volts or higher, while operating at high frequencies, typically in the range of 2-100 GHz. These types of devices may be modified for a number of types of applications, but typically operate through the use of piezoelectric polarization to generate a two dimensional electron gas (2DEG) that allows transport of very high currents with very low resistive losses. A typical HEMT includes a substrate, which is formed from sapphire, silicon, or SiC, a GaN layer formed over the substrate, an AlGaN layer formed over the GaN layer, two spaced ohmic electrodes and a gate electrode formed therebetween on the AlGaN layer. Thus, a typical HEMT is a planar device meaning that current between its two power electrodes travels in a lateral direction.
The specific on resistance of a planar HEMT that exhibits, for example, a 300V breakdown voltage is approximately 1/100 that of a silicon-based device with a vertical geometry of the same voltage rating. Thus, a planar HEMT is a good candidate for power applications. However, these conventional devices block voltage only in one direction.
Due to a strong need for more efficient circuit topologies in applications such as PDP and PFC, it is desirable to have a bidirectional semiconductor device that is capable of high current, low on resistance and high voltage applications in order to reduce the number of devices.